Failed to create component "MetroTextBox" in C# Visual Studio

I am trying to create a POS System using C# in Visual Studio. Then, I decided to apply the Metro UI Framework to my project. But whenever I use it, this same error appears:

I tried everything like adding this in my code:

using MetroFramework.Forms;using MetroFramework;

But I still got an error. Please help me solve this, I am new to C# in Visual Studio.